The aims of this protocol are to assess the kinetics of carbon dioxide accumulation and elimination in hypercapneic and eucapneic patients with sleep disorders, and calculate changes in body carbon dioxide stores during sleep and after awakening. The protocol also aims to relate changes in body carbon dioxide stores to ventilation and ventilatory responsiveness in hypercapneic and eucapneic patients during sleep and awakening. The influence of body size and metabolic rate on carbon dioxide kinetics during sleep and after awakening will also be examined.